Create hash maps implementation

hash maps implementation

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+#include <bits/stdc++.h>
+using namespace std;
+
+// template for generic type
+template <typename K, typename V>
+
+// Hashnode class
+class HashNode {
+public:
+	V value;
+	K key;
+
+	// Constructor of hashnode
+	HashNode(K key, V value)
+	{
+		this->value = value;
+		this->key = key;
+	}
+};
+
+// template for generic type
+template <typename K, typename V>
+
+// Our own Hashmap class
+class HashMap {
+	// hash element array
+	HashNode<K, V>** arr;
+	int capacity;
+	// current size
+	int size;
+	// dummy node
+	HashNode<K, V>* dummy;
+
+public:
+	HashMap()
+	{
+		// Initial capacity of hash array
+		capacity = 20;
+		size = 0;
+		arr = new HashNode<K, V>*[capacity];
+
+		// Initialise all elements of array as NULL
+		for (int i = 0; i < capacity; i++)
+			arr[i] = NULL;
+
+		// dummy node with value and key -1
+		dummy = new HashNode<K, V>(-1, -1);
+	}
+	// This implements hash function to find index
+	// for a key
+	int hashCode(K key)
+	{
+		return key % capacity;
+	}
+
+	// Function to add key value pair
+	void insertNode(K key, V value)
+	{
+		HashNode<K, V>* temp = new HashNode<K, V>(key, value);
+
+		// Apply hash function to find index for given key
+		int hashIndex = hashCode(key);
+
+		// find next free space
+		while (arr[hashIndex] != NULL
+			&& arr[hashIndex]->key != key
+			&& arr[hashIndex]->key != -1) {
+			hashIndex++;
+			hashIndex %= capacity;
+		}
+
+		// if new node to be inserted
+		// increase the current size
+		if (arr[hashIndex] == NULL
+			|| arr[hashIndex]->key == -1)
+			size++;
+		arr[hashIndex] = temp;
+	}
+
+	// Function to delete a key value pair
+	V deleteNode(int key)
+	{
+		// Apply hash function
+		// to find index for given key
+		int hashIndex = hashCode(key);
+
+		// finding the node with given key
+		while (arr[hashIndex] != NULL) {
+			// if node found
+			if (arr[hashIndex]->key == key) {
+				HashNode<K, V>* temp = arr[hashIndex];
+
+				// Insert dummy node here for further use
+				arr[hashIndex] = dummy;
+
+				// Reduce size
+				size--;
+				return temp->value;
+			}
+			hashIndex++;
+			hashIndex %= capacity;
+		}
+
+		// If not found return null
+		return NULL;
+	}
+
+	// Function to search the value for a given key
+	V get(int key)
+	{
+		// Apply hash function to find index for given key
+		int hashIndex = hashCode(key);
+		int counter = 0;
+
+		// finding the node with given key
+		while (arr[hashIndex] != NULL) { // int counter =0; // BUG!
+
+			if (counter++ > capacity) // to avoid infinite loop
+				return NULL;
+
+			// if node found return its value
+			if (arr[hashIndex]->key == key)
+				return arr[hashIndex]->value;
+			hashIndex++;
+			hashIndex %= capacity;
+		}
+
+		// If not found return null
+		return NULL;
+	}
+
+	// Return current size
+	int sizeofMap()
+	{
+		return size;
+	}
+
+	// Return true if size is 0
+	bool isEmpty()
+	{
+		return size == 0;
+	}
+
+	// Function to display the stored key value pairs
+	void display()
+	{
+		for (int i = 0; i < capacity; i++) {
+			if (arr[i] != NULL && arr[i]->key != -1)
+				cout << "key = " << arr[i]->key
+					<< " value = "
+					<< arr[i]->value << endl;
+		}
+	}
+};
+
+// Driver method to test map class
+int main()
+{
+	HashMap<int, int>* h = new HashMap<int, int>;
+	h->insertNode(1, 1);
+	h->insertNode(2, 2);
+	h->insertNode(2, 3);
+	h->display();
+	cout << h->sizeofMap() << endl;
+	cout << h->deleteNode(2) << endl;
+	cout << h->sizeofMap() << endl;
+	cout << h->isEmpty() << endl;
+	cout << h->get(2);
+
+	return 0;
+}